Since Light emitting diodes (LEDs) have the advantage of low production cost, simple structure, less consuming power, small size and easy installation, they are widely applied in light sources and display devices. In the market of blue-light light emitting diode, AlGaInN light emitting diodes gain more attentions then others.
Traditionally, an AlGaInN LED epitaxy structure is first formed on a substrate, and then a conductive substrate is bonded to the AlGaInN LED epitaxy structure by an adhesive layer. The substrate is removed subsequently. To obtain the AlGaInN LED epitaxy structure of high quality, the preferred material of the substrate is sapphire. Traditionally, the sapphire substrate may be removed from the AlGaInN LED structure by using a laser beam. The laser beam passes through the sapphire substrate, and decomposes the n-type semiconductor layer of the AlGaInN LED epitaxy structure, contacting the substrate, into Ga and N2. Then, Ga is melted by heat of a designated temperature, making the sapphire substrate easily removed from the AlGaInN LED epitaxy structure. During the removing step, the adhesive layer might be decomposed, if the laser beam ever illuminates the adhesive layer, making the conductive substrate separating from the AlGaInN LED epitaxy structure. This is a possible drawback.
Yoo et al. of U.S. Pat. No. 6,818,531, which disclosed a method for manufacturing vertical GaN LED, has overcome the drawback mentioned above. Referring to FIG. 1, an AlGaInN LED epitaxy structure 125 has a residue 125a of an n-type semiconductor layer. A conductive substrate 131 is bonded to the AlGaInN LED epitaxy structure 125 by an adhesive layer 124. As a laser beam is employed on lower surface of the substrate 121 to remove the substrate 121 from the AlGaInN LED epitaxy structure 125, the residue 125a of the n-type semiconductor layer prevents melting of the adhesive layer 124, and avoids peeling between the conductive substrate 131 and the AlGaInN LED epitaxy structure 125. However, according to the method disclosed in U.S. Pat. No. 6,818,531, the thickness of the residue 125a of the n-type semiconductor layer should be so controlled as to ensure that the laser beam would not pass through the substrate to the adhesive layer 124. The residue 125a of the n-type semiconductor layer must be easy to remove as well. Therefore, the etching parameters must be controlled carefully to ensure the thickness of the residue 125a of the n-type semiconductor layer.
In addition, as the laser beam is employed on the sapphire substrate, the increase of the strain between the adhesive layer 124 and the AlGaInN LED epitaxy structure 125 results in instability of the AlGaInN LED epitaxy structure, which also causes peeling between each layer of the epitaxy structure.